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The effects of chloride ion binding on the photochemical properties of sensory rhodopsin II from Natronomonas pharaonis

Paper ID Volume ID Publish Year Pages File Format Full-Text
29854 44444 2014 10 PDF Available
Title
The effects of chloride ion binding on the photochemical properties of sensory rhodopsin II from Natronomonas pharaonis
Abstract

•Cl− binds to NpSRII, even in detergent.•The binding of Cl− to NpSRII depends on the pH of the solvent.•Cl− binding induces several changes in the photochemical properties of NpSRII.•Cl− binding allows the initial proton release from Asp193 through its proper pKa control.•The Cl− binding site is assigned to the area near Arg72 and Asp193.

Whether Cl− binds to the sensory rhodopsin II from Natronomonas pharaonis (NpSRII) that acts as a negative phototaxis receptor remains controversial. Two previous photoelectrochemical studies using SnO2 transparent electrodes and ATR–FTIR demonstrated that Cl− binding affects the photoinduced proton release from Asp193 in phospholipid (PC)-reconstituted NpSRII (Iwamoto et al., 2004; Kitade et al., 2009). In this study, we investigated the effects of Cl− on the photochemistry of NpSRII solubilized by detergent (DDM). Even under these conditions, Cl− could bind to NpSRII with a Kd of approximately 250 mM; this value is ∼10-fold larger than that in the PC membrane. The binding of Cl− to NpSRII depended on the pH of the medium. In addition, Cl− binding induced the following effects: (1) a small red shift in the absorbance spectrum originating from the partial protonation of Asp75, (2) the formation of an interaction through a hydrogen-bonding network between Asp75 and Asp193, which is a proton-releasing residue, (3) several changes of the kinetic behavior of the photocycle, and (4) a photoinduced initial proton release from Asp193. The pKa values of Asp193 at various Cl− concentrations were also estimated. Based on the difference between the pKa values of Asp193 in Cl− bound and unbound NpSRII, the distance between the bound Cl− and Asp193 was determined to be approximately 6.1 Å, which agrees with the value estimated from the crystal structure presented by Royant et al. (2001). Therefore, the Cl− binding site affecting the photochemical properties of NpSRII is identical to the site proposed by Royant et al. (2001). This assignment was also supported by an experiment that introduced a mutation at Arg72.

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The effects of chloride ion binding on the photochemical properties of sensory rhodopsin II from Natronomonas pharaonis
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Publisher
Database: Elsevier - ScienceDirect
Journal: Journal of Photochemistry and Photobiology B: Biology - Volume 141, December 2014, Pages 192–201
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Bioengineering
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
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Price after discount Only $4.95
100% Money Back Guarantee
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